I don't have an answer but I have exactly the same problem!!
Depends on the year of the vehicle, but if it's slightly modern - absolutely. A disconnected or faulty speed sensor will not allow it shift out of 1st or 2nd gear. The cars computer has to know how fast it's traveling to determine shift points I think. I'm not familiar with your particular car, but there could be other sensors that have an effect on shifting as well.
That would depend on what year of Ford Explorer and which engine you have ( my 1995 Ford Explorer with the 4.0 liter OHV , V6 engine has ( 2 oxygen sensors )
There are sensors inside the trans, outside the trans, and on the engine that will all affect shifting.
there are sensors all over the engine, transmission, chassis, etc.
there are 4 o2 sensors
two
On a 1995 Ford Explorer : There are ( 2 ) oxygen sensors ( I believe there is one sensor in the outlet of each exhaust manifold )
A 1994 Explorer has 2 oxygen sensors, they are either screwed into the exhaust manifolds at their outlets or into the ehaust pipes near the engine.
My Chilton repair manual - engine wiring schematic shows ( 2 ) heated oxygen sensors for the 1993 Ford Explorer
4
2
( 2 ) oxygen sensors ( I BELIEVE they are in the outlet areas of the exhaust manifolds )